1. Field of the Invention
The present invention relates to magnetic heads for recording signals by applying magnetic fields perpendicular to recording media such as discs including hard layers. The present invention particularly relates to a magnetic head prevented from writing data on a recording medium during non-recording.
2. Description of the Related Art
FIG. 13 is a vertical sectional view of a known magnetic head H1. The magnetic head H1 is a type of perpendicular recording magnetic head for applying a magnetic field perpendicular to a recording medium M to perpendicularly magnetize a hard layer Ma included in the recording medium M. The magnetic head H1 has an opposed face opposed H1a to the recording medium M.
The recording medium M has, for example, a disc shape, further includes a soft layer Mb, and rotates on its center axis. The hard layer Ma is located far from the magnetic head H1 and has high coercive force. The soft layer Mb is located close to the magnetic head H1 and has high magnetic permeability.
A slider 1 is made of a non-magnetic material such as Al2O3—TiC and has an opposed face 1a opposed to the recording medium M. The rotation of the recording medium M creates an air flow, which separates the recording medium M from the slider 1 or allows the slider 1 to slide above the recording medium M. In FIG. 13, the movement direction of the recording medium M with respect to the slider 1 is referred to as an A direction.
The slider 1 has a trailing end face 1b. A non-magnetic insulating layer 2 made of an inorganic material such as Al2O3 or SiO2 lies on the trailing end face 1b. A reading section HR lies on the non-magnetic insulating layer 2.
The reading section HR includes a lower shield layer 3, a reading element 4, an inorganic insulating layer (gap insulating layer) 5, and an upper shield layer 6. The inorganic insulating layer 5 lies between the lower shield layer 3 and the upper shield layer 6. The reading element 4 is located in the inorganic insulating layer 5 and is a type of magnetoresistive device such as an AMR device, a GMR device, or a TMR device.
A first coil-insulating base layer 7 lies on the upper shield layer 6 in that order and a plurality of second coil layers 8 made of a conductive material such as Cu are arranged on the first coil-insulating base layer 7.
The second coil layers 8 are covered with a first coil-insulating layer 9 made of an inorganic material such as Al2O3 or an organic material such as a resist.
A main magnetic pole layer 10 lies on the first coil-insulating layer 9. The main magnetic pole layer 10 extends from front end face 10c of the magnetic pole layer 10 in a height direction and has a predetermined length. The main magnetic pole layer 10 extends in a track width direction (the X direction in FIG. 13) and has a width equal to a track width Tw. The main magnetic pole layer 10 can be formed by, for example, a plating process and is made of a material, such as Ni—Fe, Co—Fe, or Ni—Fe—Co, having high saturation magnetic flux density.
A gap layer 13 made of an inorganic material such as Al2O3 or SiO2 lies on the main magnetic pole layer 10.
A second coil-insulating base layer 14 lies on the gap layer 13 and first coil layers 15 made of Cu are arranged on the second coil-insulating base layer 14. The first and second coil layers 15 and 8 have end portions which arranged in the track width direction (X direction) and which are electrically connected to each other. The first and second coil layers 15 and 8 form a solenoidal coil layer that surrounds the main magnetic pole layer 10.
The first coil layers 15 are covered with a second coil-insulating layer 16 made of an inorganic material such as Al2O3 or an organic material such as a resist. A return path layer 17 made of a ferromagnetic material such as permalloy lies over the second coil-insulating layer 16 and the gap layer 13.
The return path layer 17 has a connecting section 17b. A lead layer 19 located close to the connecting section 17b extend from the first coil layers 15 in the height direction (Y direction) and lies on the second coil-insulating base layer 14. The return path layer 17 and the lead layer 19 are covered with a protective layer 20 made of an inorganic non-magnetic insulating material or another material.
In the magnetic head H1, if a recording current is applied between the first and second coil layers 15 and 8 through the lead layer 19, the current flowing between the first and second coil layers 15 and 8 induces a recording magnetic field around the main magnetic pole layer 10 and the return path layer 17. The magnetic flux φ1 of the recording magnetic field emanates from the front end face 10c of the main magnetic pole layer 10 and passes through the hard layer Ma and the soft layer Mb. This allows a recording signal to be written on the recording medium M. The magnetic flux φ1 returns to the front end face 17a of the return path layer 17.
With reference to FIG. 14, in the magnetic head H1, which is of a perpendicular magnetic recording type, the magnetization direction of the main magnetic pole layer 10 is perpendicular to the opposed face H1a during recording. The direction perpendicular to the opposed face H1a is the same as the direction of the magnetic shape anisotropy of the main magnetic pole layer 10. Therefore, the magnetization of the main magnetic pole layer 10 is likely to be directed perpendicularly to the opposed face H1a during non-recording. This causes an unintended signal to be written on the recording medium M. A reduction in the size of the main magnetic pole layer 10 and a reduction in track width cause this phenomenon to be serious.
In order to prevent unintended writing during non-recording, a magnetic head disclosed in Japanese Unexamined Patent Application Publication No. 2004-139676 (hereinafter referred to as Patent Document 1) includes a main magnetic pole layer and an auxiliary layer which is disposed thereon and which is rendered ferromagnetic or non-magnetic by light irradiation. The auxiliary layer is made of alloy containing K, Co, Fe, C, and N. The auxiliary layer is rendered non-magnetic by irradiation with a blue beam emitted from a blue semiconductor laser or rendered ferromagnetic by irradiation with a red beam emitted from a red semiconductor laser. During recording, the auxiliary layer is rendered non-magnetic by irradiation with the blue beam such that a recording operation is not disturbed. During non-recording, the auxiliary layer is rendered ferromagnetic by irradiation with the red beam. When the auxiliary layer is ferromagnetic, an end portion of the auxiliary layer has a large volume and has closure domains. This prevents the magnetization of the end portion of the auxiliary layer from being directed perpendicularly to a face of this magnetic head that is opposed to a recording medium. Patent Document 1 also discloses that the auxiliary layer is allowed to have magnetic anisotropy in the direction (a track width direction) parallel to the opposed face such that the magnetization of the end portion of the auxiliary layer is directed in parallel to the opposed face during non-recording.
The magnetic head disclosed in Patent Document 1 has problems below. Since magnetic phase transition is allowed to occur in the auxiliary layer by irradiation with a laser beam, a magnetic recording/reproducing apparatus must include a laser beam irradiation device. This causes a complication in the apparatus. Therefore, it is difficult to reduce the size and manufacturing cost of the apparatus.
Furthermore, the magnetization of the main magnetic pole layer must be directed in parallel to the opposed face against the magnetic shape anisotropy of the main magnetic pole layer and the auxiliary layer must be ferromagnetically coupled with the main magnetic pole layer tightly. In order to comply with an increase in recording density, the main magnetic pole layer must have a smaller size in the track width direction. The reduction in the size of the main magnetic pole layer decreases the bonding area between the auxiliary layer and the main magnetic pole layer, resulting in the reduction in the ferromagnetic coupling between the auxiliary layer and the main magnetic pole layer. In addition, the reduction in the size of the main magnetic pole layer in the track width direction increases the magnetic shape anisotropy perpendicular to the opposed face. This leads to difficulty in controlling the magnetic domains present in the end portions of the main magnetic pole layer.